doc.: IEEE g Submission December 2009 Tim Schmidl, Texas Instruments Inc.Slide 1 Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [More Suggested Improvements for SUN OFDM] Date Submitted: [December 2009] Source: [T. Schmidl, A. Batra, S. Hosur] Company [Texas Instruments] Address [12500 TI Blvd, Dallas, TX USA] Voice:[ ], FAX: [ ], Abstract:[This presentation gives more suggested improvements for SUN OFDM] Purpose:[For information] Notice:This document has been prepared to assist the IEEE P It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release:The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P

doc.: IEEE g Submission December 2009 Tim Schmidl, Texas Instruments Inc.Slide 2 Real versus Complex for Lower MCS Levels We still need to decide whether to use real signals or complex signals for the lower MCS levels –Advantage of real signals is that 1 DAC chain can be eliminated for devices which only support the lowest MCS levels –Advantages of complex signals are better frequency diversity (duplicate tones have large frequency separation) when frequency spreading is used and lower peak-to-average power ratio For Option 1 the PAR for real signals (BPSK with spreading factor of 2, average of PAR for each of OFDM symbols) was 9.1 dB, while for complex signals the PAR was 7.2 dB (with phase rotations shown on the next slide) For the reason of lower PAR and better frequency diversity, it is preferable to use complex signals for all MCS levels

doc.: IEEE g Submission December 2009 Tim Schmidl, Texas Instruments Inc.Slide 3 Frequency Spreading by 4x for Option 1 Option 1 with 96 data subcarriers supports frequency spreading by 4x Data is generated on 24 data subcarriers, and each data subcarrier is copied to 3 other subcarriers Simply copying the data subcarriers increases the peak-to- average ratio versus having independent data on all 96 tones PAR for BPSK with simple copying for diversity subcarriers –with no spreading = 7.3 dB –with frequency spreading by 2 = 9.1 dB –with frequency spreading by 4 = 10.7 dB The 3 copies can be phase-rotated so that the peak-to-average ratio does not increase PAR for BPSK with phase rotation for diversity subcarriers –with no spreading = 7.3 dB –with frequency spreading by 2 = 7.2 dB –with frequency spreading by 4 = 7.2 dB

doc.: IEEE g Submission December 2009 Tim Schmidl, Texas Instruments Inc.Slide 4 Frequency Spreading by 4x for Option 1 (cont’d) Number the subcarriers from -52 to 52 including both the data and the pilots. These can be denoted d -52 to d 52. The DC subcarrier is not used. Data is generated for subcarriers 1 to 26, including 2 pilots Subcarrier 1 is copied to subcarriers 27, -52, and -26 (with phase rotations) so that maximum frequency spacing is maintained between copies d k+26 = d k * exp[j*2*pi*((k-1)/4] for k = 1:26 d k-53 = d k * exp[j*2*pi*((2*k-1)/4] for k = 1:26 d k-27 = d k * exp[j*2*pi*((3*k-1)/4] for k = 1:26

doc.: IEEE g Submission December 2009 Tim Schmidl, Texas Instruments Inc.Slide 5 Frequency Spreading by 2x for Option 1 Number the subcarriers from -52 to 52 including both the data and the pilots. These can be denoted d -52 to d 52. The DC subcarrier is not used. Data is generated for subcarriers 1 to 52, including 4 pilots Subcarrier 1 is copied to subcarrier -52 (with phase rotations) so that maximum frequency spacing is maintained between copies d k-53 = d k * exp[j*2*pi*((2*k-1)/4] for k = 1:52 The same phase rotations can be used for all 5 Options

doc.: IEEE g Submission December 2009 Tim Schmidl, Texas Instruments Inc.Slide 6 PAR’s for all Options with Phase Rotations Option 1Option 2Option 3Option 4Option 5 SF = 17.3 dB6.8 dB6.7 dB6.6 dB6.5 dB SF = 27.2 dB6.6 dB6.7 dB6.6 dB6.5 dB SF = 47.2 dB6.5 dB6.7 dB6.6 dB6.5 dB

doc.: IEEE g Submission December 2009 Tim Schmidl, Texas Instruments Inc.Slide 7 Design of STF and LTF Sequences Original Complex Sequence New Complex Sequence QPSK real sequence Option Option Option Option Option Original Complex Sequence New Complex Sequence BPSK real sequence Option Option Option Option Option PAR (dB) for STF PAR (dB) for LTF

doc.: IEEE g Submission December 2009 Tim Schmidl, Texas Instruments Inc.Slide 8 Complex LTF Sequences LTF Sequences LTF_freq(Option-1)= [0, 1,-1, 1,-1, 1, 1,-1,-1, 1,-1, 1, 1, 1, 1,-1, 1, 1, 1, 1, 1,-1, 1,-1, 1, -1, 1,-1, 1, 1,-1, 1,-1,-1,-1, 1, 1, 1, 1, 1, 1,-1,-1,-1,- 1,-1,-1, 1,-1, 1, 1,-1, 1,zeros(1,23), -1, 1, 1,-1,-1,-1,-1, 1, 1,-1,-1, 1, 1, 1,-1,-1, 1, 1,-1,-1,-1,-1,-1, 1, 1,-1,-1,-1,-1,-1, 1, 1,-1, 1,-1,-1, 1,-1, 1, 1, 1, 1,-1,-1, 1, 1,-1, 1, 1,-1, 1, 1] LTF_freq(Option-2)= [0,1,-1, 1, 1,-1, 1,-1,-1, 1,-1, 1, 1,-1,-1, 1, 1,-1,-1,-1,-1,-1, 1,-1,-1,-1, 1, zeros(1,11), -1,-1,-1,-1, 1, 1, 1,-1, 1,-1, 1,-1, 1, 1,-1,-1,-1, 1, 1,-1, 1, 1, 1,-1,-1,-1] LTF_freq(Option-3)= [0, -1,-1, 1,-1, 1, 1,-1,-1, 1, 1,-1,-1, 1, zeros(1,5), 1,-1, 1,-1, 1, 1, 1, 1, 1, 1, 1, 1,-1] LTF_freq(Option-4)= [0, -1, 1, 1, 1,-1,-1,-1, 0, 1,-1, 1, 1,-1, 1, 1] LTF_freq(Option-5)= [0, -1, 1,-1, 0, 1, 1, 1]

doc.: IEEE g Submission December 2009 Tim Schmidl, Texas Instruments Inc.Slide 9 Complex STF Sequences STF Sequences STF_freq(Option-1) = sqrt(104/24)*[0, 0, 0, 0,-1, 0, 0, 0,-1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,-1, 0, 0, 0,-1, 0, 0, 0, 1, 0, 0, 0,-1, 0, 0, 0, 1, 0, 0, 0,-1, 0, 0, 0, 1, 0, 0, 0,-1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,-1, 0, 0, 0,-1, 0, 0, 0,-1, 0, 0, 0,-1, 0, 0, 0,- 1, 0, 0, 0,-1, 0, 0, 0,-1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,-1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,-1, 0, 0, 0] STF_freq(Option-2) = sqrt(52/12)*[0, 0, 0, 0, 1, 0, 0, 0,-1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,-1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,-1, 0, 0, 0,-1, 0, 0, 0,-1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0] STF_freq(Option-3) = sqrt(26/6)*[0, 0, 0, 0,-1, 0, 0, 0, 1, 0, 0, 0,-1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0] STF_freq(Option-4) = sqrt(14/6)*[0, 0,-1, 0, 1, 0,-1, 0, 0, 0, 1, 0, 1, 0, 1, 0] STF_freq(Option-5) = sqrt(6/2)*[0, 0,-1, 0, 0, 0, 1, 0]

doc.: IEEE g Submission December 2009 Tim Schmidl, Texas Instruments Inc.Slide 10 Possible Solutions to Doppler within a Packet  Differential modulation introduces new MCS levels which require extra implementation effort and testing, interoperability issues, and up to 3 dB loss in SNR  Decision-directed channel estimation is shown to work for IEEE a with the same fixed pilot structure (4 pilots) with over 1000 Hz Doppler. Channel estimates need to be updated throughput the packet. The loss due to channel estimation is < 0.5 dB even with 460 Hz Doppler. See  Pilot hopping introduces no additional pilot overhead and does not require decision-directed channel estimation.  If we use pilot hopping, then the implementer can choose to use either decision-directed or pilot-only channel estimation for coherent demodulation.

doc.: IEEE g Submission December 2009 Tim Schmidl, Texas Instruments Inc.Slide 11 Simulations for IEEE a System  Coherent demodulation is shown to work for IEEE a with the same fixed pilot structure (4 pilots) with over 1000 Hz Doppler. Channel estimates need to be updated throughput the packet. The loss due to channel estimation is < 0.5 dB even with 460 Hz Doppler. The paper also shows that if the channel estimates are not updated during the packet the performance is poor. See Simulation for a with 460 Hz Doppler. Channel estimates not updated throughput packet. Channel estimates are updated throughput packet.

doc.: IEEE g Submission December 2009 Tim Schmidl, Texas Instruments Inc.Slide 12 Staggered Pilot Structure The cyclic prefix is 1/4 of the useful part of the OFDM symbol, so this limits the delay spread that can be tolerated in the system For Option 2 we can use 3 sets of pilot tones: –If we number the subcarriers for pilot/data as -26 to 26 with the DC unused –Pilot Set 1: –Pilot Set 2: –Pilot Set 3: The pilot sets can be repeated for 3 OFDM symbols to enable averaging over interference/noise before computing new channel estimates Limiting the total number of pilot tones minimizes the computational complexity and memory required for channel estimation LTF Set1 Set2 Set3 Set1 time Set1 Set2 Set3

doc.: IEEE g Submission December 2009 Tim Schmidl, Texas Instruments Inc.Slide 13 Staggered Pilot Structure for All Options For Option 1 we can use 3 sets of pilot tones –If we number the subcarriers for pilot/data as -52 to 52 with the DC unused –Pilot Set 1: –Pilot Set 2: –Pilot Set 3: For Option 2 we can use 3 sets of pilot tones: –If we number the subcarriers for pilot/data as -26 to 26 with the DC unused –Pilot Set 1: –Pilot Set 2: –Pilot Set 3: For Option 3 we can use 3 sets of pilot tones: –If we number the subcarriers for pilot/data as -13 to 13 with the DC unused –Pilot Set 1: -7 7 –Pilot Set 2: –Pilot Set 3: For Option 4 we can use 2 sets of pilot tones: –If we number the subcarriers for pilot/data as -7 to 7 with the DC unused –Pilot Set 1: –Pilot Set 2: 2 6 For Option 5 we can use 2 sets of pilot tones: –If we number the subcarriers for pilot/data as -3 to 3 with the DC unused –Pilot Set 1: -3 1 –Pilot Set 2: -1 3